The present invention relates generally to fetal monitoring devices and, more particularly, to a disposable, non-invasive, self-adjusting tocodynamometer used to monitor uterine activity during labor.
The procedure of monitoring and analyzing uterine contractions, during both pregnancy and labor, yields significant information concerning the condition of the fetus as well as the advancement of labor. Such a procedure is useful both during routine pregnancies and especially during difficult pregnancies, those which have increased risk to the health of the fetus, to systematically evaluate fetal stress. Information indicating fetal distress during pregnancy, labor, and delivery will prompt remedial action, including caesarean delivery, which may save the fetus from harm and even death. Thus, contraction frequency, duration, intensity, and resting tone are now monitored as part of accepted, standard, obstetrical procedure.
The fetal monitors widely used to monitor the uterine activity of pregnant women, as well as the condition of the fetus while in the uterus, are typically quite sophisticated. Examples of currently available fetal monitors include the FetaScan from International Biomedics, Inc.; the Corometrics 115; and the Hewlett-Packard 8040A. Regardless of their sophistication, however, fetal monitors require a device or element to actually sense the uterine contractions. In a contraction, the abdomen hardens, and the shape of the abdomen changes, in part because the muscles in the anterior ligament of the uterus pull it forward during the contraction.
One example of such a sensing element is a catheter which is capable of measuring uterine activity within a uterine cavity itself. U.S. Pat. No. 3,599,628 issued to Abbenante et al. is an example of such a sensing element. Such devices are invasive and position sensitive; they must be positioned adjacent to the fetus for good results. Thus, movement of the fetus will often affect the results adversely.
Other devices can sense uterine activity externally and non-invasively. The advantages offered by those devices, known as tocodynamometers, have caused them to be widely used with fetal monitors. Tocodynamometers measure the hardness of the abdominal wall, which is an indication of uterine activity, through various mechanical elements. The tocodynamometer is held adjacent to the patient's abdomen, usually by a belt-like device, in the vicinity of the fundus (the top of the uterus). The tocodynamometer is initialized by setting the recording level so that it is near zero between contractions. The output of the device is transmitted to the fetal monitor through a pressure transducer, the transducer converting the pressure change information received from the tocodynamometer to an electrical signal which it delivers to the fetal monitor.
Existing tocodynamometers require frequent adjustment as the fetus moves in the uterus. Such adjustment and the weight of the devices cause discomfort for the patient. Tocodynamometers now in use also have other disadvantages, including their high cost, their fragile structures, and the difficulty and expense of cleaning and repairing them after use.
An example of another assembly for monitoring uterine activity is disclosed in U.S. Pat. No. 4,989,615 issued to Hochberg. The Hochberg assembly uses a relatively flat bladder-element, coupled with a resilient insert. The bladder and insert combination render the assembly less effective, if not inoperative, on patients having substantial amounts of soft tissue in the abdominal area. The excess soft tissue between the uterine muscle and the bladder and insert interferes with the assembly's sensitivity to contractions. Thus, the Hochberg assembly is not effectively functional for all patients--and may especially experience problems when used on obese patients.
U.S. Pat. No. 3,945,373, issued to Tweed et al., discloses an example of a tocodynamometer which has an adjustable, patient-contacting member potentially effective for use with obese patients. The disclosed device has a threaded shaft with the patient. contacting member disposed at one end of the shaft. The shaft can be adjusted up or down like a screw. Although adjustable, the tocodynamometer has several practical drawbacks, including: (1) the cost of manufacturing the complicated, electro-mechanical device, and (2) the risk of patient discomfort as the shaft impinges the abdomen.
To overcome the shortcomings of the existing devices for sensing uterine activity and transmitting information to a fetal monitor, a new, external, non-invasive tocodynamometer is provided. The general object of the present invention is to minimize the manufacturing costs of the assembly while meeting the patient's needs. By reducing manufacturing costs, the tocodynamometer becomes disposable. A related object is to provide a disposable device, therefore, which eliminates the cost and time required to clean and repair non-disposable devices. Another specific object is to assure a continually functional device, especially for obese patients, by providing increased sensitivity. Still another object is to increase patient comfort by reducing both the weight of the tocodynamometer and the number of adjustments necessary to assure optimum performance.